Many of his patients who are considered obese are unable to accurately perceive their activity levels, he said. Heavier people tend to overestimate their total exercise because they aren't used to it.

Grant often recommends those patients use a fitness monitor, which ranges in cost from $60 to $200 and can be worn on a wrist, collar or belt. The devices can help by encouraging consumers to increase activity levels and making them aware of their sleep habits.

"I've had a fair degree of success using these bands as external motivators for patients who just don't really understand what's on the table as far as what they are doing," he said.

Observing the data changes their behavior, he said. The fitness monitors also motivate consumers to work toward the general goal of moving 10,000 steps a day — roughly five miles.

Grant, whose analysis of studies focusing on sleep and fitness monitors was the focus of his recent webinar "Personal Fitness Monitors — What They Tell You About Your Health," says the devices help show patterns in behavior, providing a baseline for users. Most patients are more sleep deprived than they realize, he said.

The devices use accelerometers to measure motion. When set in sleep mode, they sense even subtle movement. They can track whether a user is awake, in light sleep or deep sleep, often during REM, or rapid eye movement, a time of restorative sleep in which the body is essentially paralyzed except for the muscles outside the eye and the diaphragm.

By viewing how often the user wakes up and during what part of the night, Grant said he gains insight into whether someone is suffering a sleep disorder.

But fitness monitors have limitations when it comes to sleep. Grant said he can "fake out" the devices by staying very still. They also don't explain why patients are not sleeping, or what's causing sleep fragmentation.

While the sleep results can be considered basic, Grant cautioned that fitness monitors may give patients a false sense of security. Studies show one device overestimated the amount of sleep in adults, while another underestimated sleep in children.

6 Tips for restful slumber

1 Turn off the TV, computer, iPad, mobile phone and other devices that may be shining in the room, vibrating or causing unnatural light or sounds. Your body is sensitive to its surroundings and will not be able to fully rest in such a heightened state.

2 Set the right mood and temperature. When preparing for bed, set the lights on their lowest settings. Install a dimmer switch to your bedroom lights and make sure the temperature is set between 65 and 68 degrees.

3 Be consistent in your sleep pattern. Try to go to bed at the same time every night, including Saturday and Sunday. You will be programming yourself to become tired at a certain time of the day, which will allow you to fall to sleep faster.

4 Avoid eating and caffeine. It's best to avoid caffeine within six to eight hours of going to bed. Finish eating at least two to three hours before bedtime. Also, minimize the amount of alcohol you drink prior to bedtime. Having too much of any drink will result in possible late-night or early morning bathroom trips.

5 Try exercising four to six hours in advance of bedtime. Not only will working out help relieve your day's concerns, but burning away all that energy will naturally cause your body to feel tired and ready to relax.

A recent Iowa State University study found that accuracy varies among personal fitness monitors.

• In all, researchers tested eight different models. Gregory Welk, professor of kinesiology, said the majority of devices provided a reasonably accurate estimate of calories burned, within 10 to 15 percent.

• The BodyMedia FIT was the top performer with a 9.3 percent error rating, which is comparable to research models, Welk said. The Fitbit Zip showed a 10.1 percent error rating, followed by Fitbit One with 10.4 percent.

• To test the devices, 30 men and 30 women wore all eight monitors during a 69-minute workout that included a series of 13 different activities, ranging from writing at a computer and playing Wii tennis to playing basketball and running. Participants also wore a portable metabolic analyzer that researchers used for comparison to test the accuracy of each device.

• The study did not address the sleep feature of the devices. Investigators have begun a second phase of the fitness monitor research, testing new models and reviewing measurements for strength training.